LM741 connections with signal generator

[iMo]

People in electronics communicate with help of schematics diagrams.
Show us your schematics and describe how do you perform the measurement.

[Gazmon]

People in electronics communicate with help of schematics diagrams.
Show us your schematics and describe how do you perform the measurement.

The schematic is posted  in the first few posts !!

[iMo]

Show us your schematics with the exact wiring and how is your generator and the  oscilloscope wired.
Do not expect the forum members will do for you.
They will certainly try to help you, but you have to provide the exact inputs.

[Gazmon]

Point taken sorry

R1 is 2k
R2 is 10k

My input signal is 9v pos/neg, appreciate this is slightly low , but it’s a start

Sigen connections are positive to pin 3 lm741
Sigen connection negative to pin 2 lm741

Appreciate the info request , and apologies
Oscilloscope is connected ground and to the output pin of LM741

[rstofer]

Hi

I have attached my scope reading as they appear with my sigen input, why is my amplitude not correct to my outputted sigen signal

Just outputting a triangle waveform and cycling through the others

I’m connected as an non inverting I think , positive sigen connected to the -

I'm pretty sure you want negative feedback and you absolutely don't want a differential input.  You do not connect your generator between pins 2 and 3.

Signal goes in on +, generator ground connects to scope ground and battery ground.  Negative feedback like you posted in Reply 3.  R1 as shown in Reply 3 also connects to that common ground point.

Your gain is awfully high considering how little swing you can have with your limited voltages.  For a first cut, I would drop the gain to 1 and see that I got the same voltage swing out as in.

You would be building a non-inverting amplifier:
https://www.electronics-notes.com/articles/analogue_circuits/operational-amplifier-op-amp/non-inverting-amplifier.php

[iMo]

The Gain of your opamp is set to

A = 1 + R2/R1 = 1+ 10k/2k = 6

With 9Vpp (??) input signal from your generator you overdrive the opapm.

With +/-9V batteries the max opamp's output you may get could be 14Vpp (+/-7V) max for example.
With A = 6 the max opmap input (your generator output) could be max 2.2Vpp (peak to peak) therefore.
Also mind your generator's DC level must be 0V (your input signal must be centered around 0V) otherwise 2.2Vpp will not fit into 14Vpp output range.
Better set the generator's output to 500mVpp at the beginning and watch the output.

Also the generator shall be connected between + input and GND (GND is the middle of the +/-9V batteries).

PS: in case it is your first experiment with 741 always use some protection resistors (1k-10k in series with input and output) at the opamp's input and output, or use coupling capacitors (as in my schematics above) in order not to smoke your 741.

[Gazmon]

Ok I will adjust my connections

And again apologies for the lack of info above at first

Will post my results , Thanks again everyone

[iMo]

For example:
R3 and R4 are protection resistors (1k-10k).
The input is 5kHz square, -0.5V to +0.5V, 1Vpp.
Output is 6Vpp (-3V to +3V).

PS: the second picture is 3kHz 2.2Vpp sine (-1.1V to +1.1V) input.

The 3rd picture is the same 2.2Vpp sine signal but DC shifted to +0.5V (centered around +0.5V). You may see the output does not fit into the opamp's output range anymore (with +/-9V batteries).
The output is clipped at +8V (the max swing).

[Gazmon]

Ok I will add a 1k- 10k to the output connection in series then and at the input

[iMo]

I've updated above the examples and pictures - with that settings you have to see the same on your o'scope screen..

[Gazmon]

I’m guessing that from my experiments based in the above my output readings will also vary based on my protection resistors fitted

Is this correct?

I am getting a sine wave now 👍

[iMo]

You should not see any visible difference with or without the protection resistors.

[rstofer]

I’m guessing that from my experiments based in the above my output readings will also vary based on my protection resistors fitted

Is this correct?

I am getting a sine wave now 👍

No, see Rule 1 here:


No current flow, no voltage drop.  Now, in reality there is a tiny current flow (see datasheet 'Bias Current') that could be as high as 1.5 uA.  This would drop 1.5V if the input resistor was 1 Mohm but at 1k, it drops 0.0015V and that's worst case.

Watch Dave explain op amps, it will help.

[Gazmon]

The video is spot on thank you

If I want to check some measurements with my multimeter based my setup and the info in previous posts, I can do this between 0v and the output pin ?

[rstofer]

In general, that ground between the two batteries is the reference voltage for ALL measurements.  There is simply no other point that works.  Ground is ground for everything:  Scope, signal generator, DMM, everything.